Building a Turing machine

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daniel_i_l
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As a summer project I was thinking of building an entirely mechanical Turing machine - possibly with Lego. Has anyone attempted this? Does anyone have any advice on how to design this?
Thanks.
 

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  • #2
sylas
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As a summer project I was thinking of building an entirely mechanical Turing machine - possibly with Lego. Has anyone attempted this? Does anyone have any advice on how to design this?
Thanks.
That's a great idea... but, yes, it has been done, by students at Aarhus University. They have a blog about it, at Lego of Doom, including a video of it in operation.

Lego%20005.jpg


Cheers -- sylas
 
  • #3
daniel_i_l
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Yes, but they used a computer chip to store the transition table and compute the next state. I want mine to be entirely mechanical.
 
  • #4
sylas
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Yes, but they used a computer chip to store the transition table and compute the next state. I want mine to be entirely mechanical.
That would be very cool! Good luck.
 
  • #5
Danny Hillis wrote about building a tinker toy computer, and if I recall correctly, he said it was a big mistake not to include error correction. Keep that in mind when you build yours. And do share your results!
 
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Hi there, new to the forums, and I have a question...

What exactly is a turing machine? I saw it one here and visited wikipedia. Is it basically a device that can perform a logical sequence of instructions with or without the need for a computer processor. So a completely mechanical turing machine would run on some sort of fuel, but actions and triggers etc. would be mechanically stored somehow?, like via a complex series of gears or switches?

Glad to be hear and I would love to hear anyone's feedback.
 
  • #7
CRGreathouse
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What exactly is a turing machine? I saw it one here and visited wikipedia. Is it basically a device that can perform a logical sequence of instructions with or without the need for a computer processor.
It's a mental experiment. There's no point* to building a 'standard' mechanical Turing machine, though every computer simulates one in a certain sense.

* Except for a cool project like this, of course.
 
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That's a great idea... but, yes, it has been done, by students at Aarhus University. They have a blog about it, at Lego of Doom, including a video of it in operation.

Lego%20005.jpg


Cheers -- sylas
WoW I saw the video, so cool.

I would love to see the fully mechanical lego turing machine
 
  • #9
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I assume you are meaning a mechanical universal turing machine, in which case it sounds great :) If you get it done, please post videos of it working :)

I believe the analytic and difference engines designed by Babbage were entirely mechanical as well, although I don't think they were quite universal turing machines (namely, not completely general purpose).
 
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Is a Turing machine the same as a universal Turing machine?
 
  • #11
sylas
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Is a Turing machine the same as a universal Turing machine?
A universal turning machine is a set of transition tables for a turing machine. It means any other turing machine can then be encoded on to the tape, and simulated.

A concrete representation in lego becomes a universal machine given the right transition tables. If the transition table is maintained on a computer chip, as in the Aarhus machine, there is no problem making it into a universal turing machine, although actually encoding a non-trivial machine onto the lego tape might be too big. If the transition tables are maintained in lego as well, then the universal machine transition tables might be more than you'd like to build.

Cheers -- sylas
 
  • #12
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Yup, the other way of thinking of it is that a universal turing machine is able to act as though it were any other turing machine given the right input. If you encoded each turing machine as a number Tn then a universal turing machine U would act on an input U(n) after which it would function as Tn

It's basically what all computers emulate :) The encoding for a universal turing machine is pretty hefty though. I think I've seen a decimal encoding of a universal turing machine number (so an n in Tn specifying a universal turing machine) run on for several a5 pages.
 
  • #13
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I seem to recall some rendition of a UTM that required only 22 or 24 quintets. (I haven't looked at this stuff since Turing died.)
 
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The main problem, as I see it, is where will you put the infinite-length tape?
 
  • #15
daniel_i_l
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Hi,
In the end lego was too expensive so I used carboplast, popsicle sticks, plastic bottles, rubber bands and a glue gun. Here's the result:

The turing machine in the movie can run down the track and flip bits according to a program determined by the wiring. Currently it can only execute simple programs because it doesn't have external memory. But that's theoretically simple to add because I'd just have to build another identical unit that operates on one bit only for each bit of memory.
 
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